It is important to prepare preferentially
oriented films to enhance
charge carrier transport in the optoelectronic device applications.
For the promising optoelectronic material of CsPbBr3, obtaining
its thin films with preferred crystal orientation is highly desirable
yet challenging. Herein, (121)-oriented CsPbBr3 perovskite
films were successfully obtained by using HBr as the additive for
PbBr2 precursor solution in the two-step solution method.
Detailed investigations indicate that microstructure tailoring of
PbBr2 films via HBr additives plays a crucial role in achieving
(121)-oriented CsPbBr3 films. Theoretical calculations
and experimental measurements demonstrate high carrier mobility in
(121)-oriented CsPbBr3 films, which accords well with photovoltaic
tests that the (121)-oriented CsPbBr3 film shows short-circuit
photocurrent density as much as 1.68 times than the (101)-oriented
one. In comparison with the (101)-oriented CsPbBr3 solar
cell, the champion power conversion efficiency of the (121)-oriented
CsPbBr3 solar cell increases from 2.56 to 6.91% owing possibly
to its higher coverage and carrier mobility. This work not only develops
a pathway to prepare compact (121)-oriented CsPbBr3 films
but also highlights the importance of crystal orientation engineering
in perovskite films for high-performance optoelectronic devices.
Both phase and morphology of perovskite films are very important for high‐performance optoelectronic devices. Although a two‐step method based on CsBr ethylene glycol monomethylether (EGME) solution can prepare pure‐phase CsPbBr3 films, they have a poor morphology due to excessive Ostwald ripening. Herein, a bi‐solvent engineering strategy is demonstrated to simultaneously optimize phase and morphology of CsPbBr3 films in a two‐step solution method, which uses the bi‐solvents of EGME and isopropanol (IPA) instead of EGME for CsBr solution at the second step. Optimizing the volume ratio of bi‐solvents and immersion time can control the Ostwald ripening effectively and result in pure‐phase, compact, and smooth CsPbBr3 films. Finally, the prepared films are applied to perovskite solar cells (PSCs) with a structure of fluorine‐doped tin oxide (FTO)/compact TiO2 (c‐TiO2)/CsPbBr3/carbon. In comparison with EGME, the champion power conversion efficiency (PCE) of devices from EGME/IPA bi‐solvents increases from 3.57% to 7.29% owing mainly to higher coverage, smoother surface, and lower trap density of CsPbBr3 films from EGME/IPA bi‐solvents. This work provides a simple and efficient method for the preparation of high‐quality CsPbBr3 films.
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